The proposed research program consists of 6 closely related interdisciplinary projects which focus on one or more aspects of the dilemma between nutritional goals and metabolic tolerance of low birth weight infants. Project A addresses questions concerning growth as well as biochemical evidence of protein sufficiency or excess incident to feeding either human milk or artificial formulas differing in protein and energy content. Questions concerning the effects of these diets on immunological development are addressed in Project B. Other projects focus on differences in body ccmposition (Project C) as well as energy expenditure (Project D) incident to the various diets. In these projects, relationships between anthropometric variables and measured body composition as well as relationships between measured body composition and that predicted from studies of energy balance will be identified. Project B explores questions related to metabolism of intravenously administered amino acids in an effort to design a mixture of amino acids which will result in a completely normal plasma amino acid pattern. The final project includes in vitro studies addressing a number of questions concerning theoretical immunological hazards or benefits related to the cellular components of human milk. A human milk bank is proposed both to provide a safe source of milk for infants enrolled in the various projects and to provide basic practical information concerning various aspects of milk banking. The program also includes biomathematical and administrative support components. In total, this program will provide new information concerning possible benefits and drawbacks in feeding low birth weight infants with human milk. It will also provide much needed data for the overall improvement of nutritional management of these infants.